This invention relates to adaptive arrays, and more particularly to techniques for stabilizing the gain of an adaptive array on a desired signal while maintaining nulls on interferers.
Consider an adaptive array on a rotating platform. It can collect data over a coherent processing interval to estimate the statistics of interference plus noise and produce a weight to attenuate it. As the antenna rotates, the beam formed will have a response to the target or clutter that varies. This modulation reduces the ability of clutter cancellation and target detection. There are currently no methods that address this issue.
Another situation arises for an adaptive array in a jamming environment that varies with time. For example, time variations can arise from jammer motion, antenna motion, or jammer waveform variations. The adaptive array beamsteering weights must be updated periodically to maintain nulls on the jammer, which introduces a time variation in the antenna pattern. This will modulate the desired signal and clutter.
This invention provides a solution to these problems.
This invention stabilizes the gain of an adaptive array on a desired signal, while maintaining nulls on interferers. This is accomplished by multiplying the adaptive weight by a complex scalar that varies as the array rotates, or as the adaptive weights are updated to maintain nulls in a changing jammer field. This ensures that the response to a signal at a known direction is held constant during the rotation, or as the weights are updated. The invention is useful even in systems where the rotation or update is rapid.
A phase-stabilized adaptive array system for a rotating sensor array is described. The system includes an antenna array, a plurality of signal channels coupled to the antenna array, each for producing a channel signal, each channel including adaptive signal weighting apparatus for weighting the channel signal by a channel weight. The system further includes combining apparatus for combining the weighted channel signals to form a beam signal. In accordance with an aspect of the invention, the system further includes phase compensation apparatus for applying phase compensation weights to the array signals or the beam signal which vary in dependence on the antenna position such that the response to a signal at a known direction is held substantially constant while the sensor array is rotated, or as the weights are updated.
A further aspect of the invention is in a method for operating an adaptive array comprising the steps of rotating the antenna array with respect to a target, providing a plurality of signal channels coupled to the antenna array, each for producing a channel signal, adaptively weighting each channel signal by a channel weight, and combining the weighted channel signals to form a beam signal. The method further includes, for phase stabilizing the response to a target at a given angular position, the step of applying phase compensation weights to the array signals or the beam signal which vary in dependence on the antenna position such that the response to a signal at a known direction is held substantially constant while the sensor array is rotated, or as the weights are updated.